The static view of the heart as a terminally differentiated organ incapable of any regeneration has undergone considerable change with the discovery of multipotent cardiac progenitor cells (CPCs) residing within the heart. However despite their existence, it is apparent that the regenerative ability of resident cardiac progenitors is not sufficient to regenerate myocardium and prevent ventricular dysfunction after myocardial infarction. The signals regulating differentiation of resident CPCs are currently unclear. The long term,goals of the project are to identify and understand factors that determine myogenic differentiation of resident CPCs after myocardial injury. We show here that secreted frizzled related protein 2 (Sfrp2), a Wnt modulator, inhibits cardiomyogenic differentiation of P19CL6 cells, a murine embryonal cell line, well studied for mammalian myogenesis. We demonstrate that resident CPCs express Sfrp2 and cardiomyocytes increase Sfrp2 expression following hypoxic injury. We have thus hypothesized that Sfrp2 in an autocrine or paracrine fashion inhibits differentiation of resident CPCs. The specific aims include: 1) Determining the effects of Sfrp2 on myogenic differentiation of CPCs, 2) Determining whether alteration of Sfrp2 expression in CPCs or in the heart after myocardial injury affects myocardial regeneration and 3)Determining whether Sfrp2 modulates canonical Wnt signaling in mediating its effects on differentiation of CPCs. We have isolated CPCs from the adult mouse heart and will initially determine the effects of Sfrp2 on myogenic differentiation of these cells in vitro. Subsequently, we will use RNA interference techniques to alter Sfrp2 expression on isolated CPCs as well as in the heart following injury to elucidate the role of Sfrp2 in regulating myogenesis in vivo. Finally, we will use molecular and biochemical assays to interrogate the effects of Sfrp2 on canonical Wnt signaling in CPCs. The candidate wishes to work on cardiac regeneration as a long term goal;this project thus serves as an ideal platform to transition to independence. Duke University Medical Center provides a rich collaborative and integrated environment for training of physician-scientists. Relevance: Owing to the limited regenerative capacity of the heart, heart disease often results in dreaded sequelae of congestive heart failure. This proposal aims to determine how stem cells within the heart can be coaxed to form new heart muscle and could lead to the design of novel regenerative therapies of heart disease.